In a wideband wireless communication systems the bandwidth of a transmission is usually is much larger than the coherent frequency bandwidth. This implies that the channel signatures in different frequency subbands may be mutually uncorrelated. When a first communication device, such as a base station, does not have information pertaining to the channel signature in all frequency subbands, the use of beamforming techniques at the first communication device when transmitting to a second communication device, e.g., a specific or particular mobile station, becomes less reliable. To feedback all estimated channel coefficients in all frequency subbands would require too much overhead in a transmission from the second communication device to the first communication device. The term “uplink” is used herein to refer to transmissions from the second communication device to the first communication device and the term “downlink” is used to refer to transmissions from the first communication device to the second communication device.
In time division duplex (TDD) systems, the uplink channel coefficients matrix is strongly correlated with the downlink channel coefficients matrix. Thus, there is an opportunity to exploit this property in order to derive knowledge about the channel between the first communication device and the second communication device in any frequency subband.